Navmesh gone on runtime

i have a problem with navmesh rebuild at runtime.
at the viewport, when P is pressed, i can see the navmesh fine… and at runtime everything is a ok…
but that is default settings…

when i changed the recastnavmesh : agent radius to 10
then heres the problem starts. whn P is pressed, everything looks fine… green everywhere expected…
but when played / runtime, there is no navmesh…

dynamic is set and for rebuild on runtime is checked…

but when on runtime, consoled rebuildnavigation, the navmesh rebuilds… then everything is ok …

try to instantly rebuild on “BeginPlay”

how do i do that?.. with bleprint?